If Congress doesn’t act to extend relief from the alternative minimum tax by the end of 2012 – an important element of the fiscal cliff – the IRS said Tuesday that it would have to enforce the AMT against about 33 million households ...

"If there is no AMT patch enacted by the end of the year, the IRS would be forced to operate the 2013 tax filing season based on the expiration of the AMT patch,” the acting IRS commissioner, Steven Miller, wrote in a letter to GOP Sen. Orrin Hatch of Utah on Tuesday. “There would be serious repercussions for taxpayers.”

The AMT was created in the 1960s to make sure that very wealthy people who accumulate a lot of deductions still paid some tax. Over the years, it has begun to hit many middle-class households, at least on paper, in part because it’s not indexed for inflation.

AMT relief is renewed every year. Maybe someday they'll just index it for inflation.